This invention relates in general to methods of pyrolysis and, more particularly, to a pyrolysis method in which an organic material, such as biomass or city waste, is pyrolyzed in a two-bed type pyrolysis system which includes a fluidized bed type pyrolysis reactor and a combustion reactor to obtain a high-energy fuel gas as the pyrolysis gas.
Methods have been proposed for the gasification of municipal waste and biomass to produce high energy fuel gas. However, biomass and municipal waste generally have a high water content and when such material is fed to a pyrolysis apparatus a large amount of heat is required for pyrolysis thereof since much heat is consumed in the vaporization of the water.
For example, in a partial oxidation type pyrolysis method in which an organic material is pyrolyzed utilizing heat generated through the burning of part of the material, it is necessary to supply large amounts of air to the material, to oxidize and burn the same. Accordingly, the recovered fuel gas contains N.sub.2 from the air and CO.sub.2 remaining in the reaction zone after the material has been combusted, thereby resulting in the fuel gas having a relatively low calorific value.
In a two-bed type pyrolysis operation, a heat medium is heated with the heat generated by the combustion of char and tar which are by-products of the pyrolysis of a material. The heat medium is circulated between a fluidized bed type pyrolysis reactor and a combustion to thereby obtain the heat required for pyrolyzing the material. In such two-bed type pyrolysis operations, it is necessary that a large amount of recovered fuel gas in addition to char and oil be burned in order to supply sufficient heat to the material. Therefore, this pyrolyzing method also has a relatively low gas recovery rate.
The fuel gas recovered in pyrolyzing methods is utilized as a power source. Thus, the fuel gas is burned such, for example, as by a gasoline or a gas turbine or the like. However, the combustion exhaust gas is merely discharged to the ambient atmosphere or, since it has a high temperature, can be used to heat water.